1,3-Dioxacyclopentane, hereinafter referred as dioxolane, is a derivative of ethylene glycol which is used industrially and can be prepared by reacting ethylene glycol with an aqueous formaldehyde solution in the presence of acid catalysts such as sulfuric acid, boron trifluoride, zinc chloride or acid ion exchangers. Pure dioxolane can be isolated from the reaction mixture using various separation methods, in particular by distillation or extraction.
Dioxolane is used, in particular, as comonomer in the polymerization of trioxane to form polyoxymethylene copolymers.
The by far most frequently used method of separating liquid mixtures into fractions or pure components is distillation or rectification. The separating action of this powerful process is based on mass transfer between a gaseous phase and a liquid phase which are conveyed in direct contact in countercurrent to one another.
DE A 1 279 025 discloses a process for the continuous purification of a dioxolane-comprising reaction mixture from the reaction of ethylene glycol with formaldehyde in the presence of acid catalysts, in which a crude dioxolane which still comprises relatively large amounts of water, unreacted formaldehyde and relatively small amounts of acid and alcohol, e.g. formic acid and methanol, is firstly obtained by distillation and is fed in gaseous form into a distillation column in which an azeotropic mixture of dioxolane and water comprising not more than 10% by weight, generally about 7% by weight, of water is distilled off at the top. The azeotropic mixture is cooled to about 20-40° C. and is treated in countercurrent with alkali metal hydroxide and/or a concentrated aqueous alkali metal hydroxide solution, by means of which it is largely freed of water and other impurities. After the alkali treatment, it is fractionally distilled to give purified dioxolane having an extremely low water content of 50 ppm or less via the bottom of the column. The process has the disadvantage that a plurality of distillation columns are necessary to obtain pure dioxolane, resulting in corresponding capital, operating and in particular energy costs.